Power actuated vehicle steering systems



Dec. 11, 1956 E E. G. STAUDE 2,773,351

POWER ACTUATED VEHICLE STEERING SYSTEMS Filed Dec. 30, 1955. 2Sheets-Sheet l 5 r Z I J3 IIImImm 2 mnmn 21 mm 1 (gm N f W .II I lllllllll Z3 III-m Tim an lulu-um 2 jazz 07: mi G'Jtazzafe,

Dec. 11, 1956 E. ca. STAUDE 2,773,351

POWER ACTUATED VEHICLE STEERING SYSTEMS Filed Dec. 50,. 1955 2Sheets-Sheet 2 .J o o I "J2 z o o i we or.

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PQWER ACTUATED VEHICLE STEERING SYSTEMS Edwin Gustave Staude, LosAngeles, tlalif.

Application December 30, 1955, Serial No. 556,608

12 Claims. (Cl. 60--52) The present invention relates generally to apressure fluid operated power steering system and has particularreference to control over the steering effort generated in the system.

it is a general object of the invention to provide a power steeringsystem embodying a power cylinder, means for actuating this cylinder,and means for controlling the steering effort generated in the powercylinder in accordance with the vehicle engine speed.

Another object is to provide control means eflecting the generation ofpower assist at idle or low vehicle engine speeds, smooth and gradualbut progressively increasing reduction in power assist generated as thevehicle engine speed increases uniformly to intermediate speed, andfurther progressive reduction of the power assist generated in the powercylinder as high vehicle engine speeds are attained.

A further object of the invention is to provide control means responsiveto rate of flow of fluid supplied from a pump driven by the vehicleengine and passing through the power cylinder, and thus responsive tovehicle engine speed.

A more detailed object of the invention lies in the provision of acontrol valve for the pressure fluid supplied to the power cylinderconnected in a vehicle steering system, for causing a gradual andprogressive reduction in the volume and pressure of fluid supplied tothe power cylinder as the vehicle engine speed increases, thus reducingprogressively (at a gradually increased rate) the proportion supplied bythe power cylinder of the total effort required to move the groundwheels and restoring ground feel to the vehicle steering system.Accordingly, the power cylinder is actuated to supply maximum power tothe power steering system for steering at low vehicle speeds or when thevehicle is at .a standstill, while at increased speeds the volume andpressure of fluid supplied to the power cylinder decreasesprogressively, such that at high vehicle speeds suflicient fluidpressure is available to cause the power cylinder to follow themovements of the steering mechanism produced by manual operation, tooperate as a means to dampen the;,stee ring mechanism, and to providepower in the event of an. emergency.

Thus it is an object to provide a valve adapted to be located in thepower steering system between the pump and the power cylinder, forprogressively reducing the pressure and volume of fluid supplied fromthe pump to the power cylinder as the vehicle speed increases, bybypassing pressure fluid in progressively increasing flow past the powercylinder in accordance with the rate of flow and pressure of fluidsupplied by the pump.

This application is a continuation-in-part of co-pending applicationSerial No. 528,644, filed August 16, 1,955.

The objects of the invention generally set forth together with otherobjects and ancillary advantages are obtained by the construction andarrangement shown by way of illustration in the accompanying drawings,in which:

Figure 1 is a plan view of a valve embodying the features of the presentinvention;

nited States Patent 2,773,351 Patented Dec. 11, 1956 Fig. 2 is avertical section taken substantially in the plane of line 22 in Fig. 1;

Fig. 3 is a detail view of an element of the valve illustrated in Fig.1;

Fig. 4 is a vertical section taken substantially in the plane of line4-4 in Fig. l;

Fig. 5 is a section taken substantially in the plane of line 5-5 of Fig.1;

Fig. 6 is a schematic view of a power steering system embodying thefeatures of the present invention with the valve of Fig. 1 incorporatedin the system.

While the invention is susceptible of various modifications andalternative constructions, there is shown in the drawings and will beherein described in detail, an illustrative embodiment. It is to beunderstood, however, that it is not thereby intended to limit theinvention to the specific form disclosed. In fact, certain modificationswill be hereinafter described whereby the scope of the invention maybe'more clearly understood, and it is intended to cover allmodifications, alternative constructions, and equivalents falling withinthe spirit and scope of the invention as expressed in the claims.

Referring more particularly to the drawings, the form of the inventionthere shown for purposes of illustration is embodied in a power steeringsystem of the type shown in Fig. 6. ln general, this system is linkagetype with a power cylinder 11 connected to the front drag link orsteering linkage 12 of a motor vehicle steering assembly, although itwill be understood the invention may be incorporated in power steeringsystems of other types. The illustrative system also incorporates a pumpP, driven by the vehicle engine, which pump constitutes a sourceproviding a variable flow of pressure fluid for the power cylinder orcontrolled device to generate effort to move the road wheels W. 1

In the present instance, in the power steering system between the pumpand the power cylinder a valve 113 is employed to automatically controlthe volume and pressure of fluid supplied from the pump P to the powercylinder 11.

Conventional power steering systems, of which the linkage type shown inFig. 6 is one, include the power cylinder connected in the vehiclesteering system for supplementing manual effort supplied through asteering Wheel S and gear G to turn the road wheels W.

In general, pressure fluid is conducted from the pump P to the intake 1'of the power cylinder ll, and the constantly flowing stream of pressurefluid delivered by the pump P circulates within the housing containingthe valve V, the pipes and r communicating with the chambers on eachside of the piston p, and to the return line to the pump P. Manualrotation of the shaft s by means of the steering wheel S results in aslight axial movement of valve V from a neutral position {as shown) toeffect a change in the pressure conditions in the chambers on each sideof :the piston, the flow into pipes l and r and the respective chambersbeing throttled by the valve V to obtain the pressure differential fordriving the piston p and generating power assist to move the roadwheels.

It is well recognized that the effort required to move the road wheelsof a motor vehicle is substantially greater when the vehicle is at astandstill or moving at low speeds, for example while parking, than athigher driving speeds. A point is soon reached as the vehicle speedincreases where the effort required could easily be supplied exclusivelyby manual means.

In the operation of the power steering system shown in Fig. 6, which isconventional in this respect, the pump P which delivers fluid underpressure to drive the power cylinder, is a variable delivery type pumpdriven directly by the vehicle engine. Hence, the output of fluid fromthe pump l is proportional to the rate of rotation thereof and to therate of rotation of the vehicle engine. Consequently, as the vehiclespeed increases the output of the pump correspondingly increases.

The pump P is generally designed such that when driven by an idlingvehicle engine fluid is delivered to the power steering system at a rateof flow and pressure which will produce appreciable force to turn theroad wheels. As the vehicle engine speed increases above idling,however, the increased rate of flow and pressure of fluid delivered fromthe pump overdrives the power cylinder. In a system with no compensatingmeans included, this results in loss of ground feel at increased enginespeeds.

Ground feel may be defined as sensitivity to force acting against thewheels by the road surface. The presence or absence of ground feel isimportant at driving speeds when if the wheels are turned too sharply,the vehicle may skid or roll over, depending on the condition of theroad surface.

The present invention is concerned with means for reducing the pressureof fluid supplied to the power cylinder at driving speeds, and means forinsuring that sufflcient fluid volume and circulating pressure isdirected to the power cylinder so as to eliminate any tendency of thepower unit to drag at these speeds and also so as to provide emergency,instantaneously available power to assist the manual means in turningthe road wheels.

Accordingly, in one illustrative form of this invention, means areprovided for controlling the flow and pressure of fluid supplied to thepower cylinder '11 in accordance with the vehicle engine speed.Furthermore, the means provides for reducing the proportion supplied bythe power cylinder of the total effort required to move the road wheelsat a progressivelyincreasing rate as the vehicle speed is raised, toeffect restoration of ground feel to the vehicle steering system.

In the present instance, this means comprises the control valve 13located in the line between the pump P and reservoir R, and the powercylinder 11 of the power steering system. For connection in the system,the control valve 13 includes a valve housing 20 provided with spacedparallel tubular members 21, 22 and 23, 24, having threaded extremitiesfor convenience in connecting the valve with conduits 25, 26 extendingto the power cylinder 11 and conduits 27', 28 extending to the pump P.The central body portion of the housing member 20 is open interiorly toprovide communication between the opposite tubular members, which formin the valve housing, parallel inlet and outlet passages 29, 30,respectively, extending through the body of the valve housing 20.

In addition to the parallel inlet and outlet passages, the body of thevalve housing 20 is provided with a bypass passage arranged tocommunicate between the inlet and outlet passages 29, 30. In the presentinstance, the by-pass passage is formed within a sleeve 31 pressed intoposition or otherwise secured in place in the body of fthe housing 20.

Thus, inlet and outlet passages 29, 30, respectively, are formed in thebody of the valve housing 20 and means are provided for connecting thevalve housing with conduits extending to the pump and power cylinder ofthe power steering system and hence, in the line between the pump andthe power cylinder. By means of the connected between the pump P and thepower cylinder 11.,

Furthermore, the means are so arranged that as the rate of flow of fluidsupplied to the power cylinder through 4 the control valve increases,the by-pass passage is gradually and smoothly opened to admit fluidthereto and bypass the power cylinder in progressively increasingamounts. Consequently, as the vehicle speed increases, the pressure offluid supplied to the power cylinder is progressively reduced, until apoint is reached where substantially the entire effort required to movethe road wheels is supplied exclusively through the manual operatedmeans.

As shown in Figs. l-5 of the drawings, this means comprises a rotatablebalanced valve element 32 mounted within the sleeve 31 and provided witha central bore 33 substantially circular in cross-section.

One end of the bore 33 communicates with a cavity 35 in the valvehousing 20 which connects the opposite tubular members 23, 24respectively, forming the outlet passage 30 in the housing 20 of thecontrol valve.

The inlet passage side of the control valve housing 20 is also openinteriorly to connect the opposite tubular members 21, 22 respectively,making up the inlet passage 29 through the valve housing. The rotatablebalanced valve element 32 extends completely across the space formed inthe inlet passage side of the valve housing, and abuts the screw cap 36which serves to prevent the valve element from axial motion andeffectively retains the valve element in place within the sleeve 31. Thevalve element 32 also extends across the cavity 35 in the outlet passage30, and means are provided thereon to actuate the valve element 32 inaccordance with the rate of flow of fluid passing through the outletpassage. Thus within the housing 20, the portion of the valve element 32which extends across the cavity 35 is notched at 37 to carry a vane 38adapted to be moved in accordance with the pressure and rate of flow offluid passing through the outlet passage 30. In the preferred form ofthe invention illustrated, the vane 38 is fastened to the valve element-32 by means of rivets 39 or the like, and is formed of a substantiallyrectangular member corresponding generally to the interior configurationof the cavity 35 and abutting the sides of the cavity and thus againstthe inner surface of a cover 40 closing the outlet passage side of thevalve housing, and fastened in place by bolts 41.

In order to provide for the passage of fluid through the cavity 35 andoutlet passage 30, past the vane 33, the end of the vane terminates ashort distance from the peripheral wall of the cavity 35. In the form ofthe invention illustrated, the vane may swing from one position againsta stop 42, carried by one wall of the cavity, to a second positionagainst a stop 43 formed by a flange extending completely across thecavity in the outlet passage. The position of the vane against the stop42, as shown in Fig. 4, corresponds to the closed position of the valveelement, and normally the vane is held in this position by means of aspring 44, which is selected to exert sufiicient force to prevent thevane from moving until a certain minimum pressure and rate of flow offluid is reached in the outlet passage, which may readily be determinedfor the particular power steering system in which the invention is to beincorporated.

The position of the vane against the flange 43 (dotted Fig. 4)corresponds to the open position of the valve element disposed in theby-pass passage, and in the illustrative form of the invention shown,gradual uniform rotation of the valve element upon or accompanyinggradual and uniform increase in the rate of flow and pressure of fluidpassing through the outlet passage, causes a smooth and progressiveincrease in the rate of admission of fluid through the by-pass passagefrom the inlet passage to the outlet passage in the valve housing.

In the present instance, pressure fluid from the inlet passage isadmitted to the bore 33 within the valve element 32, by way of passagesformed in the sleve 31 and in the valve element 32. The valve elementhas been described hereinbefore as a balanced valve element, andaccordingly the sleeve 31 and the portion of the valve element extendingacross the inlet passage are provided with oppositely disposed passagesadapted to register upon the valve element being rotated to open theby-pass passage. As noted previously, the by-pass passage is opened uponmovement of the vane away from the stop 42, such movement accompanyingincrease in rate of flow and pressure of fluid passing through theoutlet passage 30.

More specifically, the valve element is drilled and counterbored toprovide radial passages 45 extending outwardly from the centrallongitudinal bore 33 therein and adapted for registration with openings46 in the sleeve 31. By counterboring, the mouth of each of the passages45 disposed on opposite sides of the valve element 32 is enlarged toencompass the openings 46 formed in the sleeve 31 anl providing thepassage therethrough for admission of fluid to the interior of the valveelement.

In the construction and arrangement illustrated, fluid is admitted inprogressively increasing amounts from the inlet passage to the bore 33formed in the valve element 32. In the operation of the valve depictedin the drawings, uniform rotational movement of the valve element 32causes the passages 45 therein to be gradually thrown into communicationwith the openings 46 in the sleeve, thus increasing the effective areaof the passage communicating with the inlet passage 39 and extending tothe bore centrally of the valve element and forming the by-pass passage.Upon uniform movement of the valve element 32, progressively increasingamounts of fluid are admitted into the bore within the valve element 32to bypass the power cylinder connected in the power steering system.

Accordingly, the valve element 32 is mounted for rotation within thevalve housing between a normally closed position (Figs. 2 and 4) and anopen position. The vane 38 is held against, the stop 42 by means. of aspring 44 normally urging the valve closed and the radial passages 45are then out of registration with the openings 46 in the sleeve 31. Theopen position of the valve follows movement of the vane counterclockwiseas viewed in Fig. 4 to the dotted position against flange 43, where thepassages and openings in the valve element and sleeve respectively arein registration. In the closed position of the valve, with the admissionof fluid through the bypass passage interrupted, the portions of thevalve element 32 which might be termed cut-oft portions 50, 51,circumferentially between the mouths of the passages 45, block theopenings as in the sleeve 31 and prevent the admission of fluid to thebypass passage formed by the bore 33 through the valve element.

In the present instance, the openings in the sleeve and the passagesformed in the valve element overlap in progressively increasing amountsincident to rotation of the valve element in order that a uniform rateof 111- crease ,of fluid delivered from the pump accompanying uniformrate of increase in engine speed causes fluid to be admitted through thebypass passage in progressively increasing amounts and the pressure offluid supplied to the power cylinder to be reduced at a. rate greaterthan the rate of increase in engine speed or the rate of increase offluid delivered by the pump. To facilitate further obtaining anon-linear relation between the output of the pump and the amount offluid by-passed past the power cylinder, hereinbefore stated in terms ofprogressive increase or decrease, the radius of the inside peripheralsurface 52 of the cavity 35 in the outlet passage, is constructed from adifferent center than the axis of rotation of the vane. Thus as the vanemoves counter-clockwise along the are 53 shown in dotted lines in Fig. 4the clearance between the end of the vane and the peripheral wall of thecavity decreases. Accordingly, a unit increase in pressure and rate offlow of fluid at high levels of pump output produces a greater movementof the valve element than the same unit increase at low levels of pumpoutput. It is noted, however, that even in the extreme counterclockwiseposition of the vane as viewed in Fig. 4, clearance is provided betweenthe end of the vane and the peripheral wall of the cavity 35 to permitthe flow of fluid past the vane and prevent the creation of a backpressure in the outlet passage to unduly aifect the operation of thepower unit.

In the operation of a system having the control valve incorporatedtherein, little or no eflect is produced upon the rate of flow andpressure of fluid supplied to the power cylinder at low levels of pumpoutput. As the pump output increases, however, the valve element isrotated to admit fluid from the inlet passage through the by-passpassage to the outlet passage, effectively by-passing the powercylinder. Thus at low engine and pump speeds fluid at a pressure andrate of flow determined by the operating characteristics of the pumpwill be supplied to the power cylinder, and the operation of the powersteering system will be as in a conventional system. As the engine speedincreases, the output of the pump corresondingly increases and the rateof flow and pressure of the fluid passing into the power cylinder,through the return line and thus through the outlet passage of thecontrol valve, increases correspondingly, to move the vane disposed inthe outlet passage counterclockwise as shown in Fig. 4 and to graduallyadmit fluid in progressively increasing amounts through the by-passpassage of the control valve.

Accordingly, the effort produced by the power cylinder upon increase invehicle engine speed, is progressively and rapidly reduced at a rategreater than the rate of reduction of total effort required to turn theroad wheels as the vehicle speed increases. The portion supplied by thepower cylinder of the total eifort required to move the road wheels iscorrespondingly reduced, until a point is reached, as for example, withthe vane against the stop 43 in the counterclockwise position depictedin dotted lines in Fig. 4, where substantially the entire effortrequired to move the road wheels is supplied by the manually operatedsteering wheel and gear.

The vehicle speed at which the control valve begins actuation, may bedetermined by the strength of the spring 44, the width and length of thevane 38, and the configuration of the cavity 35 in which the vane ismounted.

Other modifications, to produce readily predictable changed operatingcharacteristics of the valve, may be effected Without departing from thepresent invention, and it is intended that the scope of the presentinvention be limited only by the appended claims.

I claim as my invention:

1. In a fluid volume control valve for a motor vehicle power steeringsystem having a power unit operated by a pump driven by the engine ofthe motor vehicle, the combination comprising a control valve housinghaving inlet and outlet passages and a by-pass passage therebetween,said inlet passage being provided for connection in the line between thepump and the intake to the power unit, and said outlet passage beingprovided for connection in the return line from the power unit to thepump, valve means in said by-pass passage, and means responsive to rateof flow of fluid from the pump for opening said valve means to draw oflfluid through said by-pass passage from the inlet passage at relativelyhigh vehicle engine speeds and correspondingly relatively high rate offlow and for closing said valve means to cut oft said by-pass passage atrelatively low vehicle engine speeds and correspondingly relatively lowrate of flow of fluid from the pump, whereby to reduce the flow of fluidsupplied to the power unit from a maximum supplied at said relativelylow engine speeds when said valve means is closed.

2. In a fluid volume control valve for a motor vehicle power steeringsystem having a power unit operated by a pump driven by the engine ofthe motor vehicle, the combination of a control valve housing havinginlet and outlet passages and a bypass passage therebetween, said inletpassage being provided for connection in the line between the pump andthe intake to the power unit, and said outlet passage being provided forconnection in the return line to the pump, a valve clement supported insaid by-pass passage, a vane pivotally mounted in said outlet passage inthe path of fluid passing through said passage, a resilient memberurging said vane against the pressure of the fluid, said vane forming aflow responsive actuating device for said valve element, said vaneactuating the valve element to draw off fluid through said bypasspassage from the inlet passage during periods of relatively high rate offlow of fluid from the pump, and to cut ofi said by-pass passage duringperiods of relatively low rate of flow, whereby to provide for maximumpressure of fluid supplied to the power unit during said periods ofrelatively low rate of flow and reduction in pressure of fluid from saidmaximum pressure as rate of flow increases.

3. In a fluid volume control valve for a motor vehicle power steeringsystem having a power unit operated by a pump driven by the engine ofthe motor vehicle, the combination of a control valve housing havinginlet and outlet passages and a by-pass passage therebetween, said inletpassage being provided for connection in the line from the pump to theintake to the power unit and said outlet passage being provided forconnection in the return line from the power unit, a valve elementsupported in said by-pass passage, a chamber formed in said housingcommunicating with said outlet passage, a vane pivotally mounted in saidchamber, said vane forming a flow responsive actuating means for saidvalve element for opening said valve element and drawing off fluidthrough said by-pass passage from the inlet passage during periods ofrelatively high rate of flow of fluid through the outlet passage, and tocut off said by-pass passage during periods of relatively low rate offlow, whereby to provide for maximum pressure of fluid supplied to thepower unit during said periods of relatively low rate of flow andreduction in pressure as rate of flow increases.

4. In a fluid volume control valve for a motor vehicle power steeringsystem having a power unit operated by a pump driven by the engine ofthe motor vehicle, the combination of a control valve housing havingspaced longitudinally arranged inlet and outlet passages and atransverse by-pass passage therebetween, said inlet passage beingprovided for connection in the line from the pump to the intake to thepower unit and said outlet passage being provided for connection in thereturn line from the power unit, chambers formed in said housing to en--large said inlet and outlet passages and arranged adjacent theextremities of the by-pass passage, a valve element supported in saidby-pass passage including a sleeve mounted in the passage extending intothe chamber provided to enlarge the inlet passage, said sleeve havingopenings for communicating between the chamber and the inside of thesleeve, a rotatable member supported inside said sleeve to extend intothe chamber formed to enlarge the oulet passage, said member having abore therein communicating with said chamber and openings between thebore and the outside of the member adapted to be'moved into and out ofalignment with the openings in said sleeve, a vane in the chamber formedto enlarge said outlet passage, said vane being carried by saidrotatable member, a spring urging said vane and said rotatable member toa cut-off position of the valve element where the openings in the memberand the openings in the sleeve are out of alignment, whereby increase offlow of fluid through the chamber formed to enlarge the outlet passagepast said vane rotates said vane against the spring to bring intoalignment the openings in said sleeve and said member, to open the valveelement and draw off fluid through the bypass passage to the outletpassage.

5. In a fluid volume control valve for a vehicle power steering systemhaving a power unit connected to the vehicle steering system operated bya pump driven by the engine of the vehicle, the combination comprising acontrol valve housing having inlet and outlet passages and a by-passpassage therebetween, said inlet passage being provided for connectionin the line from the pump to the intake to the power unit and saidoutlet passage being provided for connection in the return line from thepower unit, a normally closed valve element supported in said by-passpassage, and means for actuating said valve element responsive to therate of flow of fluid passing through said control valve housing, foropening said valve element progressively and drawing oif fluid throughsaid by-pass passage from the inlet passage in progressively increasingamounts as the vehicle engine speed increases above a predeterminedminimum speed to reduce the pressure of fluid supplied to the power unitand reduce the effort generated in the power 'unit progressively as thevehicle speed increases above said minimum speed.

6. In a fluid volume control valve for a system having a controlleddevice operated by "a source providing a variable flow of pressurefluid, the combination comprising, an intake passage for receivingpressure fluid from said source and providing a first outlet forsupplying pressure fluid to the controlled device, a return passage forreceiving exhaust fluid from the controlled device and providing asecond outlet for returning said exhaust fluid to said source, abalanced valve element located in said intake passage effective uponopening to control rate of flow of pressure fluid to said controlleddevice by diverting flow from said intake passage to said returnpassage, a movable actuating member located in said return passage andoperatively connected to said valve element, said member beingresponsive to flow of exhaust fluid from the controlled device and toflow of fluid diverted by said valve element from said intake passage,and resilient means connected to said member to urge said member into aninactive position whereby said valve element is closed.

7. In a fluid volume control valve for a system having a controlleddevice operated by a source providing a variable flow of pressure fluid,the combination comprising, an intake passage for receiving pressurefluid from said source and providing a first outlet for supplyingpressure fluid to the controlled device, a return passage for receivingexhaust fluid from the controlled device and providing a second outletfor returning said exhaust fluid to said source, a normally closed valveelement connecting said intake passage with said return passageeffective upon opening to control rate of flow of pressure fluid to saidcontrolled device by diverting flow from said intake passage to saidreturn passage, a movable vane mounted in said return passage, saidmovable vane being operatively connected to said valve element, a limitstop for said vane, and resilient means for urging said vane against,said stop to maintain said valve element normally in closed position.

8. In a fluid volume control valve for a system having a controlleddevice operated by a source providing a variable flow of pressure fluid,the combination comprising, a passage for pressure fluid providing anintake and an outlet to the controlled device, an exhaust fluid passageproviding an inlet from the controlled device and an outlet forreturning the exhaust fluid to said, source, a normally closed hollowbalanced valve element located in the pressure fluid passage andconnecting the same with the exhaust fluid passage, a movable vanelocated in said exhaust fluid passage and in the path of flow of exhaustfluid and of flow through said hollow valve element, said movable vanebeing operatively connected to said valve element, a limit stop for saidvane, and means for urging said vane against said stop to maintain saidvalve element normally in closed position.

9. In a fluid volume control valve for a system having a controlleddevice operated by a source providing a variable flow of pressure fluid,the combination comprising,

a housing having a passageway for connection in the line between saidsource and said controlled device, a by-pass passage in said housingopening into said passageway, a valve element mounted in said housing tocontrol rate of flow to said controlled device by diverting flow fromsaid source through said by-pass passage, a movable actuating member forsaid valve element subjected to flow to said controlled device andthrough said by-pass passage, said member being responsive to rate offlow and operable to actuate said valve element to reduce rate of flowto said controlled device upon increase above a predetermined velocityof flow acting against said actuating member.

10. In a motor vehicle pressure fluid operated power steering systemhaving a power unit connected to the vehicle steering linkage, and avariable delivery pump driven from the engine of the motor vehicle andproviding a source of pressure fluid for the power unit, the flow fromsaid pressure tiuid source varying in accordance with the engine speed,a flow responsive control valve for diverting fluid from the power unitonly upon the engine speed and flow from the pump attaining apredetermined rate, whereby the flow of fluid supplied to the power unitand the steering effort generated therein at engine speeds above thesaid predetermined rate is reduced from a maximum attained at saidpredetermined rate, said control valve including a by-pass for divertingfluid from the power unit, an actuating member responsive to rate offlow of fluid from the pump, and a valve element for said by-passoperated by said actuating member, said actuating memw her and valveelement being effective to open said by-pass only upon flow from thepump attaining said predetermined rate.

11. In a motor vehicle pressure fluid operated power steering systemhaving a power unit connected to the vehicle steering linkage, and avariable delivery pump driven from the engine of the motor vehicle andproviding a source of pressure fluid for the power unit, the flow fromsaid pressure fluid source varying in accordance with the engine speed,a flow responsive control valve for diverting fluid from the power unitonly upon the engine speed and flow from the pump attaining apredetermined rate, whereby the flow of fluid supplied to the power unitand the steering efiort generated therein at engine speeds above thesaid predetermined rate is reduced from a maximum attained at saidpredetermined rate, said con trol valve including a control valvehousing having a passageway for connection in the line between saidsource and the power unit, aby-pass passage in said housing opening intosaid passageway for diverting fluid from the power unit, a valve elementfor said by-pass passage mounted in said housing, and a movableactuating member for said valve element subjected to flow of exhaustfluid from said power unit and flow of fluid diverted from said powerunit through said by-pass passage, said actuating member and valveelement being effective to open said by-pass passage only upon how fromthe pump attaining said predetermined rate.

12. In a motor vehicle pressure fluid operated power steering systemhaving a power unit connected to the vehicle steering linkage, and avariable delivery pump driven from the engine of the motor vehicle andproviding a source of pressure fluid for the power unit, the flow fromsaid pressure fluid source varying in accordance with the engine speed,a flow responsive control valve for diverting fluid from the power unitonly upon the engine speed and flow from the pump attaining apredetermined rate, whereby the flow of fluid supplied to the power unitand the steering effort generated therein at engine speeds above thesaid predetermined rate is reduced from a maximum attained at saidpredetermined rate, said control valve including a housing, a by-passpassage in said housing for diverting fluid from the power unit, a valveelement for said by-pass passage mounted in said housing, a returnpassageway for connection in the return line between said source and thepower unit and into which said by-pass passage opens, and a movableactuating member for said valve element mounted in said housing so as tobe subjected to flow of exhaust fluid from the power unit through saidreturn passageway and flow of fluid diverted from the power unit throughsaid by-pass passage, said actuating member and valve element beingeffective to open said by-pass passage only upon flow from the pumpattaining said predeterminedrate.

References Cited in the file of this patent UNITED STATES PATENTS963,906 Larsson July 12, 1910 2,028,766 Ernst et a1 Jan. 28, 19362,603,065 Sarto July 15, 1952 2,707,375 Hammond May 3, 1955 2,733,662Hunter Feb. 7, 1956 2,734,589 Groen Feb. 14, 1956 FOREIGN PATENTS512,426 Great Britain Sept. 15, 1939

